Constitutively active Lyn kinase causes a cutaneous small vessel vasculitis and liver fibrosis syndrome

Neutrophilic inflammation is a hallmark of many monogenic autoinflammatory diseases; pathomechanisms that regulate extravasation of damaging immune cells into surrounding tissues are poorly understood. Here we identified three unrelated boys with perinatal-onset of neutrophilic cutaneous small vessel vasculitis and systemic inflammation. Two patients developed liver fibrosis in their first year of life. Next-generation sequencing identified two de novo truncating variants in the Src-family tyrosine kinase, LYN, p.Y508*, p.Q507* and a de novo missense variant, p.Y508F, that result in constitutive activation of Lyn kinase. Functional studies revealed increased expression of ICAM-1 on induced patient-derived endothelial cells (iECs) and of β2-integrins on patient neutrophils that increase neutrophil adhesion and vascular transendothelial migration (TEM). Treatment with TNF inhibition improved systemic inflammation; and liver fibrosis resolved on treatment with the Src kinase inhibitor dasatinib. Our findings reveal a critical role for Lyn kinase in modulating inflammatory signals, regulating microvascular permeability and neutrophil recruitment, and in promoting hepatic fibrosis.

The three patients reported are of male sex. The patients were recruited based on the clinical phenotype and on the presence of specific de novo LYN mutations (please see population characteristics below). Sex and/or gender were not considered in study design. Sex information was determined based on self-reporting and we obtained consent for sharing individual level data.
We describe three patients who have de novo variants in LYN, gene encoding Lyn kinase. Patient 1 has c.1524C>G, p.Y508*, Patient 2 has c.1523A>T, p.Y508F, and Patient 3 has c.1519C>T, p.Q507*. The three patients presented with early-onset systemic inflammation and cutaneous vasculitis, and Patients 1 and 3 also have liver fibrosis. Patient 1 is currently treated with dasatinib and etanercept, and Patients 2 and 3 are treated with etanercept only.
The index patient was referred to the National Institutes of Health for unexplained systemic inflammation, and recurrent fever and rashes and underwent trio analysis at the Clinical Center. The second patient was identified in Great Ormond Street Hospital for Children, London UK and the third patient at the University Karlova in Prague, Czech Republic. The NIH protocol enrolls parents and healthy siblings as controls as well as blood donors from the blood bank. The control experiments were conducted with blood from the patients' parents and or controls from the blood bank.
All research investigations were done as part of protocol 17-I-0016/ NCT02974595 and as such were approved by the NIAID and NIAMS/NIDDK Institutional Review Boards. For patient 3, the research investigations were also approved by the Institutional Review Board of the Second Faculty of Medicine, Charles University and University Hospital Motol.
Not applicable. No sample size was determined as we included three patients with a novel and ultra-rare autoinflammatory disease.
No data were excluded from the analyses.
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Materials
Not applicable. No random allocation was performed in the experiments with patient samples because we are reporting three patients with a novel and ultra-rare autoinflammatory disease. Experiments were conducted comparing samples from the patient with the disease-causing LYN mutation compared to controls who do not carry the LYN mutation to characterize the effect of the LYN mutation on outcomes assessed.
Blinding was not relevant for this study because we are reporting three patients with a novel and ultra-rare autoinflammatory disease.